I have successfully implemented multiple file extensions to be added as Plugin data sources to the map as feature layers. Some of them are new types and some are which are recognizable to Pro(like csv). For the new types I have created the Pro Custom Item to be started with. And for the ones which are recognizable to Pro as per the documentation there is no need. This is as per the Pro docs
File extension already in use by ArcGIS Pro (including portal, on-line, geodatabases, toolboxes, etc) cannot be overridden/extended with a custom item. This includes text files, xml files, folders, database connection files, layer files, task files, mxds, sxds, etc. Custom items defined on content types in use by ArcGIS Pro will be ignored.
I have also added multiple ways to add the data source like Context Menus, Drag and Drop and using Add Data in the Ribbon.
This is mostly achieved using interface IMappableItem and implementing the below method for the Custom Item class
public List<string> OnAddToMap(ArcGIS.Desktop.Mapping.Map map)
But how to achieve these use cases to add as feature layers for extensions like CSV. Because for CSV Add Data in the Ribbon is just adding the standalone table. And for CSV I am not sure how to add the custom context menu implementation for Add To Current Map and Add To New Map.
So the question is how to achieve these use cases for File extensions already in use by ArcGIS Pro.
Right now to add the plugin as a feature layer for CSV is just handled using Drag and Drop handler. But how to achieve all the below use cases for CSV:
"Add Data" dialog
"Add Data from Path" dialog
drag/drop of your item from the catalog window to a map
drag/drop of your item from the catalog window to the TOC
drag/drop of your item from windows explorer to a map
drag/drop of your item from windows explorer to the TOC
